package Day2025_01_20;

import java.io.IOException;
import java.net.BindException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;
import java.nio.charset.StandardCharsets;

public class UDPEchoServer {
    // 声明一个提供UDP服务的对象
    private DatagramSocket socket;

    // 通过构造方法指定服务器的端口号
    public UDPEchoServer (int port) throws SocketException {
        if (port < 1025 || port > 65535) {
            throw new BindException("端口号要在1024~65535之间.");
        }
        // 初始化UDP服务的对象
        this.socket = new DatagramSocket(port);
    }

    /**
     * 处理用户请求
     */

    public void start () throws IOException {
        System.out.println("服务器已启动.");
        // 循环处理用户请求
        while (true) {
            // 1. 使用DatagramPacket来接收用户发送的数据
            DatagramPacket requestPacket = new DatagramPacket(new byte[1024], 1024);
            // 2. 接收数据
            socket.receive(requestPacket);
            // 3. 解析收到的数据
            String request = new String(requestPacket.getData(), 0, requestPacket.getLength(), "UTF-8");
            // 4. 通过请求计算响应
            String response = process(request);
            // 5. 使用DatagramPacket封装响应的数据
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(StandardCharsets.UTF_8),
                    0, response.getBytes().length, requestPacket.getSocketAddress());
            // 6. 发送响应
            socket.send(responsePacket);
            // 7.打印日志
            System.out.printf("[%s:%d] request = %s, response = %s\n", requestPacket.getAddress().toString(), requestPacket.getPort(),
                    request, response);
        }
    }

    private String process(String request) {
        return request;
    }

    public static void main(String[] args) throws IOException {
        UDPEchoServer server = new UDPEchoServer(8888);
        server.start();
    }
}

